The present invention relates to the field of ball valves and more particularly to that type of valve which is known as a McCannaseal Ball Valve and is manufactured by the Rockwell International Corporation at Carpentersville, Ill. Ball valves have wide application in the control of fluids in various industrial applications. The construction usually takes the form of a cast valve body that defines an enclosed valve chamber having both inlet and outlet ports. Characteristically, there is provided a spherical ball valve held in valve seats that are generally located adjacent inlet and outlet ports. The valve is frequently, but not always, spring biased to urge it into firm contact with the valve seats. To permit the passage of fluid, an opening is provided across the diameter of the ball valve to provide an interconnection between the inlet and outlet ports of the valve body, when the valve is oriented or turned into that position. Various types of sealing arrangements are commonly provided to insure fluid integrity. Unlike most ball valves where the opening through the ball is along the diameter, as mentioned above, the opening, or through flow passage in the type of valve involved here is along a line parallel to the diameter but spaced therefrom. By thus displacing the flow passage, the usual spherically appearing ball valve becomes in effect a tapered ball. This latter shape permits the valve body to have a top access opening that permits the valve and valve seats to be efficaciously removed for repair and replacement as required, without removal of the entire valve assembly from its operational environment.
Since operating conditions, as well as the materials being controlled by a valve may vary significantly, the material of which the valve is constructed will be selected accordingly. Assuming that anticipated operating conditions are to be benign, then material such as plain carbon steel could be that material selected; whereas under more demanding or restrictive conditions a stainless steel or some other high alloy material may be the selection of choice. Generally, selection of materials according to sound engineering prescription will result in valve operation and life suitable for normal applications. Beyond that spectrum into which most valve usage falls, however, are those unusually demanding situations in which valve life is significantly decreased. Where a valve must handle a slurry, such as paper pulp or coal slurry for example, useful valve life is markedly reduced because of erosion of the valve body in the regions adjacent to the valve seats. When this erosion progresses far enough, the entire valve must be removed from the line and replaced. The same problem also occurs when the valve must handle highly corrosive fluids, such as many of those utilized in the chemical industry.
One example of a typical rotary plug valve is seen in Johnson, Jr. et al U.S. Pat. No. 3,211,421. In this patent a spherical valve member 52 having a spherical sealing surface 54 is located within the chamber 48 located between aligned fluid passages 46. The ball is sealed by means of the resilient mass 14 which comes into contact with the spherical surface 54. The inner wall between end walls 50 of the chamber 48 are sealed by means of the resilient O-ring 44 as the member 50 is pushed back against the other end wall of the valve casing.
Another example is that shown in U.S. Pat. No. 4,111,393 in which there is provided a seat ring 50 into which is mounted seat insert 52. An additional element that is provided is the O-ring 54 that co-acts with both the seat ring 50 and the seat insert 52 to make up a composite sealing arrangement that contacts the outer surface of ball 16.
A principal object of this invention is to provide an improved tapered ball valve in which the valve body is provided with means permitting maintenance to be performed on the valve body in such a way that the effects of corrosion and erosion can be compensated for without replacing the entire valve body.
An additional object of this invention is to provide an improved tapered ball valve in which a valve seat insert is provided that is removable for replacement to correct for erosive and corrosive damages.